Process of making paper-pulp



-- .UNITED STATWES KAJE'NT OFFICE.

RALPH H. MCKEE, or NEW YORK, N. Y., AND ANDREW A. HOLMES, F BOSTON,

- MASSACHUSETTS.

No Drawing.

hitherto known resinous woods (6, g. south-- PROCESS OF MAKING PAPER-PULP.

To all whom it may concern:

Be it knownthat we, RALPH H. MoKEE and AN1)1iEw-A, HoL.\rEs, citizens of the United States, residing at New York and Boston, in thejcounties of New York and Suffolk and States: of New Yorkfand Massachusetts,"respectively," have invented certaiiik-neni'faird useful Improvements in Process'es of Making Paper Pulp, of whichthe followingisl-a specification.

Tli's nvention relates to ,a process of makin'gpa'per pulp and has particular reference to an improved process of this character which is adapted to produce pulp from resinous woods, which is sufficiently free from resin to enable it to be used in making paper of a high grade.

For many purposes the sulfite process of making paper pulp gives the. best type of paper pulp. However, by the methods ern pines) do 'not yield to the sulfite process to give a pulp sufliciently free from resin to make a paper of good quality for most purposes, 6. 9., a bond writing paper. Such Woods are commercially only used for the.

manufacture of sulfate or soda pulp, '1'. 6., for pulp useful for wrapping paper or soft book paper, or the like.

lVe have discovered that when chipsjof such a resinous wood are extracted with a resin-dissolving solvent and the solvent removed, the remaining wood chips when subjected to the customary sulfite pulp treatment give a paper pulp which in quality compares favorably with the standard pulp made by the sulfite process from non-resinous woods, such as spruce.

As a solvent, any of the resin-dissolving solvents such as benzol or carbon bisulfi'd may be used. but we prefer to use liquid sulfur dioxid. In case such a solvent as benzol or carbon bisulfid is used, the wood chips after extraction are steamed to remove and recover the remaining portion of the solvent and then sent to the digester where they are cooked by the customary methods used to'produce soda, sulfate or sulfite pulp. Liquid sulfur dioxid has the advantage over solvents previously mentioned that it carries no fire risk, is much more cheaply produced, and the portion re maining in the chips after extraction need not be removed before the next step of cooking to a pulp when the sulfite process is Specification of Letters Patent. Pate t d N 30 1920 Application filed May 24, 1919. Serial No. 299,632

used. In fact, this residual sulfur dioxid rema ning in the chips is a distinct advantage 1n the succeeding step of sulfite pulp manufacture.

Liquid sulfur dioxid has thedisadvantage that it vaporizes at ordinary pressure and consequently must be used under a pressure sutlicient to keep it liquid during the time it is belng used to remove the resins from the chips. Distillation of the solvent from the resulting solution leaves the extractable material behind. This can then be prepared for the market by the customary methods of the art.

When sulfur dioxid is the solvent used, we prefer, although this is not a necessary procedure, to extract inthe same vessel as that in which the succeeding step of cooking is desirable. as it shortens the period of extraction and has other desirable features.

Then fill the digester with the chips and produce a partial vacuum in the digester so as to remove the larger part of the air present around and within the chips. This withdrawal of air is not essential to the process but serves to hasten the extraction and to reduce the amount of relief gases that have to be handled during the extraction process.

Sulfur dioxid in liquefied form and preferably at a somewhat elevated temperature, say one giving a pressure of 75 pounds per square inch gage pressure, is then passed into the chips. This liquid is kept in contact with the chips for a length of time, which depends on the size of the chips. Itis then pumped off and fresh sulfur dioxid introduced to complete the extraction. If necessary to remove the greater part or if desired, substantially all of the resin, a third charge of sulfur dioxid may be used but two are ordinarily suiiicient. The relief gases, if any, are piped to the acid making plant for strengthening the cooking acid.

The resulting solution of the rosin, tur- .llO

pentine and small amounts of other extractives in liquid sulfur dioxid is then distilled in. such a manner that the sulfur dioxid is recovered in liquid form for reuse, preferably being distilled under pressure. The residue consisting of rosin, turpentine, etc., and a little dissolved sulfur dioxid is then placed in a second still and distilled in such a manner as to separate the sulfur dioxid from the turpentine and leave the residue of molten rosin in the still. The molten rosin is drawn off into barrels and is ready for the market. The turpentine so produced is for many purposes satisfactory, but in other cases it can with advantage be subject to further refining, c. 9., washing with alkali and redistilling. The gas which contains sulfur dioxid, escaping from the stills is sent to the acid making plant of the sulfite pulp department to be used for strengthening the cooking acid.

The chips n the digester which have had the rosin and turpentine largely removed by the extraction effect of the liquid sulfur dioxid are now covered by the customary cooking acid used in the sulfite pulp industry except that this acid may be of less than the customary strength to the extent of the amount of the sulfur dioxid remaining 1n. the chips. The customary cooking acid to which reference is made consists of a Water solution containing approximately one per cent. of sulfur dioxid combined with lime (calculated as C2130 and four per cent. free sulfur dioxid, largely in the. form of sulfurous acid (H 30 Steam is turned on and the sulfite cooking process is carried out in the customary manner, seven to eleven hours time being required according to the character of paper to be made. The resulting pulp is washed and bleached 1n the customary manner and is ready for the manufacture of paper. Recoveries of the sulfur dioxid in the escaping gases are made in the customary manner.

The residual waste sulfite liquor can be used for the making of alcohol, etc., as described in the Letters Patent Nos. 1,273,392, 1,284,739 and 1,284,740 by one of us.

lVhile for the purpose of illustration we have described in detail the prefered practice of our process, it is to be understood that the details of procedure may be widely varied without departing from the spirit of our invention or the scope of the subjoined claims.

Having described our invention, we claim:

1. The process of making'paper pulp consisting in first subjecting resin containing wood to the action of liquid sulfur dioxid and then to the action of a pulp producing operation whereby paper pulp is produced therefrom.

2. The process of making paper pulp consisting in first subjecting resin containing wood to the action of liquid sulfur dioxid at an elevated temperature and at super-atmospheric pressure and then to the action of a pulp producing operation whereby paper pulp is produced therefrom.

3. The process of making paper pulp consisting in first subjecting resin containing wood to the action of liquid sulfur dioxid and then to the action of the sulfite process whereby paper pulp is produced therefrom.

1. The process of making paper pulp consisting in first subjecting resin containing wood to the action of liquid sulfur dioxid, separating the liquid sulfur dioxid from its dissolve-d content and subjecting the treated wood to the action of a pulp producing op eration whereby paper pulp is produced therefrom.

5. The process of producing paper pulp from resin containing wood which consists in placing the wood in a sulfite digester, subjecting it to the action of liquid sulfur dioxid, removing the main portion of the sulfur dioxid from the digester, adding sulfite liquid and subjecting the treated wood to the sulfite cooking process whereby paper pulp is produced therefrom.

In testimony whereof we aflix our signatures in presence of two witnesses.

RALPH H. MCKEE. ANDREV A. HOLMES. Witnesses;

L. V. EATON, M. B. MCDONALD. 

